1. Field of the Invention
This invention relates to heat exchangers and more particularly to an arrangement for supporting a plurality of heat exchanger tubes.
2. Description of the Prior Art
A heat exchanger, according to this description, is a device having an inlet head in fluid communication with an outlet head through a bundle of tubes. Furthermore, the tube bundle is enclosed in a shell that enables one fluid to flow into contact with the tube bundle and to absorb heat from or transfer heat to another fluid flowing through the tubes in the bundle.
Although each of the tubes of the bundle are generally secured in headers, that is, secured to the tube sheet of the header, other support is usually provided to withstand external or internal loads imposed on the heat exchanger and the tube bank. In particular, for a heat exchanger having closely spaced tubes of considerable length, for example, a once through type unit of the size commonly found in a commercial power plant, spacing means as well as support is necessary. This spacing means is provided to prevent tube displacements as a result of thermal expansion or contraction, flow induced vibration or gravity. Tube displacement resulting from, for example, thermal expansion or lack of physical support is undesirable since changes in the flow area about adjacent tubes, causes uneven heat transfer and increased pressure losses within the heat exchanger, and may result in fretting.
In the past, various supporting and spacing methods for heat exchanger tubes have been investigated. One method commonly practiced involves the use of spaced perforated plates commonly called baffle plates placed at intervals along the length of the heat exchanger. The tubes are held in the perforations and the plates are spaced at experimentally and/or theoretically determined intervals to prevent tube vibration. Other known arrangements include: wire wrapping of tubes, interweaving a flexible tubular member between the heat exchanger tubes and forming a heat exchanger tube having a bend therein in one plane to contact an adjacent tube in the same plane through a tie member.
In a once through heat exchanger of the type having tubes of considerable length closely spaced from one another, flow restriction problems are substantially accentuated by only a slight tube displacement. Furthermore, in the once through type of heat exchanger, it is presently necessary to prudently select the tube and shell material and to carefully control their respective operational temperatures to prevent excessive stresses due to different thermal expansion therebetween.
Accordingly, there is a need to provide a means for supporting, spacing and allowing thermal expansion in heat exchanger tubes, especially in commercial power plant heat exchangers of the type having tubes of a considerable length and a small diameter.